This invention relates to the destruction of hazardous hospital waste and, more particularly, to the destruction of hazardous medical waste using an electrode-less radiofrequency inductive and capacitive plasma discharges in combination with cryogenic material pre-treatment. The processing method includes breaking up the medical waste into powder using liquid nitrogen crusher/mill, exposing the medical waste in powder form to thermal RF plasma, and converting the disinfected powder into compact form. The term medical waste encompasses not only medical waste, but also veterinary waste.
A major problem facing modern society is the disposal of hazardous medical waste materials in a manner which is capable of reducing hazardous waste to compounds suitable for environmental disposal. Such suitability is, of course, defined in terms of acceptable levels of pollutants as determined by regulatory agencies. For example, regulated medical waste consists of the following categories: pathological waste; blood and blood product; contaminated “sharps”, such as needles, syringes, scalpels, blades, and broken glass; animal waste; cultures and stocks of infectious agents and associated biological; and disposable products, such as gloves. Commercial medical waste treatment technique includes steam sterilization (autoclaving), incineration and chemical disinfection. A number of attempts have been made in the prior art to destroy medical waste using microwave, RF direct heating, direct current arc discharge plasma source and RF plasma source.
Incineration of medical waste, while it does effectively sterilize it, has other consequences that can be extremely detrimental to public health. One of these is the production and emission of dioxin. The medical waste consists approximately 15% of plastic, most of which is chlorinated, such as PVC, which is more than 50% chlorine by weight. When plastic is incinerated in the presence of carbon and oxygen, it creates dioxin—considered the most carcinogenic compound known. Incinerators emit pollutants at very high rate, such as cadmium, arsenic, lead, dioxins, and furans. Emissions from these incinerators may be a bigger public health threat than improper dumping.
The autoclave (steam sterilizer) has been used in medicine to sterilize medical instruments. Similar systems are used for medical waste treatment. Typically medical waste is directed to a sealed chamber, to which steam is fed at approximately 160 degrees C., and pressure range between 100 to 500 kPa. Treatment time vary from 30 to 100 minutes. The process is simple, easy to control, and efficient against most of the microorganisms. However, the autoclaving has several drawbacks: it is expensive and time consuming; and it is not recommended for the treatment of organic solvents and reagents, as well as chemotherapy, pharmacological and pathological waste.
The idea of microwave treatment of medical waste originated in Germany in the early 1980 s, and since then it has been used in many countries. The sanitation process uses steam pre-heating with the help of microwaves. Medical waste material is shredded and granulated. After that the waste is humidified by hot steam and moved to a waste treatment chamber for 20-30 minutes (see for example, U.S. Pat. Nos. 5,223,231; 6,830,662B2). The system is totally closed, and therefore it does not cause any emissions. But the processed waste (disposal) still contains organic material, which could generate methane and other toxins during the landfill storage. Also, the microwave technology cannot be used in the case of liquid blood and hazardous chemicals and drugs.
None of these approaches have proven acceptable, due to the fact that materials released to the environment remain as unacceptable sources of pollution ([1] Alternative medical waste treatment technologies approved by California Department of Health Services, Medical waste management Program, MS7405, Jun. 18, 2004). Only plasma systems could be use to process all kinds of medical waste. Other technologies are limited.
One such attempt is disclosed in U.S. Pat. No. 7,216,593B2. This reference teaches the use of DC and/or AC plasma torches with a variable flame mounted with the vessel. The waste is introduced into the vessel in the form of solid pieces, preliminary treated by disinfectant. The plasma melts or vitrifies the inorganic portion of the waste and gasifies and dissociates the organic portion of the waste. The disadvantages of the above system are: it requires disinfectant for pre-treatment; a molten bath is necessary in order to make the system efficient, but at the same time the presence of the molten bath makes the system very inertial and increases the probability to generate dioxins at a very high rate, especially during the start-up and shut-off; and there is a high capital cost. The U.S. Pat. No. 6,551,563B1 teaches us method and systems for safely processing hazardous waste, including medical waste. The system is based on pyrolysis and includes a torch, vessel, scrubber, feeder thermal oxidizer and gas supply unit. The disadvantages of the system are that requires a separate gas supply unit and there is a short life time of the arc plasma's electrodes, due to the aggressive plasma environment (chlorine; HCl, etc.).
U.S. Pat. No. 5,762,009 teaches us plasma energy recycling and conversion (PERC) reactor and process for disposal of waste using induction coupled plasma heat source and two reaction chambers. Argon is used to create the plasma jet and convert waste to a gas.
The U.S. Pat. No. 5,943,970 teaches us the method and equipment for waste thermal destruction on the surface of the bath of melted metal. The reliable destruction of bacteria is provided, but dioxin and furans are generated, especially during system start-up and shut-off.
The integrated plasma-frequency induction process for waste treatment is described in (WO/2004/048851 Blush Wizoso Integrated Plasma-Frequency Induction Process for Waste Treatment, Resource Recovery and Apparatus for Realizing Same, Oct. 6, 2004), and is based on combined simultaneous plasma arc and direct induction heating of preliminary briquetted waste. They use oxygen injection to the molten pool and quench the synthetic gas after reactor. The drawbacks are that the presence of oxygen dramatically increases the emission of dioxin, and the efficiency of induction heating is very sensitive to the chemical composition of the medical waste. Many experimental data shows that pyrolytic destruction of hazardous waste generates flammable and potentially explosive gases, such as hydrogen and carbon monoxide, making the pyrolytic systems unsafe to operate. Because medical waste comprises a combination of different substances (plastic, glass, fabrics, etc.) and is not consistent from day by day, it is very difficult and expensive to control the oxygen/hydrogen ratio, i.e. the system could easy exceed safe levels.
The prior art plasma medical waste treatment systems suffer from a variety of shortcomings, which have prevented their widespread use in commercial applications. One shortcoming results from the fact that the waste material generally cannot be introduced directly into a plasma arc, because such introduction causes contamination of the electrodes and subsequent erratic operation of the arc. The same things happen when material is introduced directly into RF plasma discharge. The performance of the arc plasma is highly sensitive to the waste composition and flow rate. Arc electrode erosion further complicates the maintenance, operation, and stability of the system. Small scale operation of DC arc plasmas is also very inefficient due in part to the minimum gas flow rate and electric power requirements needed to strike and sustain the arc. Scaling the prior art systems for operation with different medical waste composition has proven to be difficult, requiring major system configuration changes, which are expensive to accomplish.
In summary, none of the prior art systems have provided an apparatus and method of efficient medical waste treatment to prevent pollution from medical waste, and reduce hazardous medical waste to components suitable for environment disposal.